import React, { Component } from 'react'

export default class Count extends Component {
  state = {count: 0}

  // 加法
  increment = () => {
    const {value} = this.selectNumber
    const {count} = this.state

    this.setState({
      count: count + Number(value)
    })
  }

  // 减法
  decrement = () => {
    const {value} = this.selectNumber
    const {count} = this.state

    this.setState({
      count: count - Number(value)
    })
  }

  // 奇数再加
  incrementIfOdd = () => {
    const {value} = this.selectNumber
    const {count} = this.state

    if(count %2 !== 0) {
      this.setState({
        count: count + Number(value)
      })
    }
  }

  // 异步加
  incrementAsync = () => {
    const {value} = this.selectNumber
    const {count} = this.state

    setTimeout(() => {
      this.setState({
        count: count + Number(value)
      })
    }, 500)
  }

  render() {
    const {count} = this.state

    return (
      <div>
        <h1>当前求和为：{count}</h1>
        <select ref={c => this.selectNumber = c}>
          <option value="1">1</option>
          <option value="2">2</option>
          <option value="3">3</option>
        </select>&nbsp;
        <button onClick={this.increment}>+</button>&nbsp;
        <button onClick={this.decrement}>-</button>&nbsp;
        <button onClick={this.incrementIfOdd}>当前求和为奇数再加</button>&nbsp;
        <button onClick={this.incrementAsync}>异步加</button>&nbsp;
      </div>
    )
  }
}
